This project is a study of neuropsychological dysfunction (using the Halstead-Reitan and Luria-Nebraska Neuropsychological Batteries) in patients with RDC-diagnosed schizophrenia, schizoaffective disorder, major depression, and mania who are participating in the investigations of the University of Chicago-Illinois State Psychiatric Institute Mental Health Clinical Research Center (MHCRC). Other investigators studying the same population will obtain detailed data on major aspects of clinical phenomenology, progostic variables, clinical course and outcome, thought disorder, major biochemical variables (platelet MAO and serum prolactin levels) and cortical evoked potentials, which can then be integrated with the neuropsychological data. Because of the multifaceted data collected on the patients to be studied, the relationships between neuropsychological disturbance and stage of illness can be studied with the goal of identifying clinically relevant subgroups of major psychiatric illnesses with neuropsychological evidence of brain damage. We should be able to determine how these findings are related to important clinical and biological characteristics, and integrate them into a neurologically-based etiological model for those types or subgroups of psychiatric disorders for which such an etiology may be applicable.